SOLUTION: Factor the trinomial x^2-9xy-10y^2

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Question 190252: Factor the trinomial
x^2-9xy-10y^2

Answer by jim_thompson5910(35256) About Me  (Show Source):
You can put this solution on YOUR website!

Looking at x%5E2-9xy-10y%5E2 we can see that the first term is x%5E2 and the last term is -10y%5E2 where the coefficients are 1 and -10 respectively.

Now multiply the first coefficient 1 and the last coefficient -10 to get -10. Now what two numbers multiply to -10 and add to the middle coefficient -9? Let's list all of the factors of -10:



Factors of -10:
1,2,5,10

-1,-2,-5,-10 ...List the negative factors as well. This will allow us to find all possible combinations

These factors pair up and multiply to -10
(1)*(-10)
(2)*(-5)
(-1)*(10)
(-2)*(5)

note: remember, the product of a negative and a positive number is a negative number


Now which of these pairs add to -9? Lets make a table of all of the pairs of factors we multiplied and see which two numbers add to -9

First NumberSecond NumberSum
1-101+(-10)=-9
2-52+(-5)=-3
-110-1+10=9
-25-2+5=3



From this list we can see that 1 and -10 add up to -9 and multiply to -10


Now looking at the expression x%5E2-9xy-10y%5E2, replace -9xy with xy-10xy (notice xy-10xy adds up to -9xy. So it is equivalent to -9xy)

x%5E2%2Bhighlight%28xy-10xy%29-10y%5E2


Now let's factor x%5E2%2Bxy-10xy-10y%5E2 by grouping:


%28x%5E2%2Bxy%29%2B%28-10xy-10y%5E2%29 Group like terms


x%28x%2By%29-10y%28x%2By%29 Factor out the GCF of x out of the first group. Factor out the GCF of -10y out of the second group


%28x-10y%29%28x%2By%29 Since we have a common term of x%2By, we can combine like terms

So x%5E2%2Bxy-10xy-10y%5E2 factors to %28x-10y%29%28x%2By%29


So this also means that x%5E2-9xy-10y%5E2 factors to %28x-10y%29%28x%2By%29 (since x%5E2-9xy-10y%5E2 is equivalent to x%5E2%2Bxy-10xy-10y%5E2)



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Answer:
So x%5E2-9xy-10y%5E2 factors to %28x-10y%29%28x%2By%29